The ToList operator takes all the items in the sequence and puts them in a list. Then the list is returned as an observable sequence (IObservable<IList<TSource>>). The return value of this operator differs from the corresponding operator on IEnumerable in order to retain asynchronous behavior.

The following example uses the Generate operator to generate a simple sequence of the integers (1-10). Then, the ToList operator is used to convert that sequence to a list. The IList.Add method is used to 9999 to the resulting list before each item in the list is written to the console window.